Read the following passage given below and answer the question.
Aldehydes and ketones undergo nucleophilic addition reactions. A nucleophile attacks the electrophilic carbon atom of polar carbonyl group from perpendicular to plane of \(sp^2\) hybridized orbitals of carbonyl carbon. The hybridization of carbon changes from \(sp^2\) to \(sp^3\) and a tetrahedral alkoxide intermediate is formed. This captures \(H^+\) to give neutral product. In carboxylic acids, carbonyl carbon is less electrophilic than carbonyl carbon of aldehydes and ketones.
An organic compound \(C_3H_6O\) does not give a precipitate with 2,4-dinitrophenylhydrazine and also does not react with metallic sodium. It could be:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → CH2=CH–O–CH3
Two simple tests tell the functional groups of \( \ce{C3H6O} \) apart:
2,4-DNP test — 2,4-dinitrophenylhydrazine adds to the C=O group of aldehydes and ketones and gives a yellow, orange or red solid (a 2,4-DNP derivative). No precipitate means no carbonyl group.
Sodium test — sodium liberates \( \ce{H2} \) from compounds with an O–H group, such as alcohols. No reaction means no –OH group.
Methyl vinyl ether, \( \ce{CH2=CH-O-CH3} \), has neither a C=O nor an O–H group, so it fails both tests.
Option (1) CH3CH2CHO — Incorrect. Propanal is an aldehyde, so it gives an orange 2,4-DNP precipitate.
\( \displaystyle \ce{CH3CH2CHO + H2NNHC6H3(NO2)2 -> CH3CH2CH=NNHC6H3(NO2)2 + H2O} \)
Option (2) CH2=CH–CH2OH — Incorrect. Allyl alcohol has an O–H group, so it reacts with sodium and liberates hydrogen.
\( \displaystyle \ce{2CH2=CHCH2OH + 2Na -> 2CH2=CHCH2ONa + H2 ^} \)
Option (3) CH3COCH3 — Incorrect. Acetone is a ketone, so it also gives a 2,4-DNP precipitate.
NCERT (2026-27 edition):
Addition of Ammonia and Its Derivatives – “Nucleophiles, such as ammonia and its derivatives H2N-Z add to the carbonyl group of aldehydes and ketones. The reaction is reversible and catalysed by acid. The equilibrium favours the product formation due to rapid dehydration of the intermediate to form >C=N-Z.”
Some N-Substituted Derivatives of Aldehydes and Ketones – “* 2,4-DNP-derivatives are yellow, orange or red solids, useful for characterisation of aldehydes and ketones.”